1. Technical Field
This invention relates to an apparatus for providing a uniform feed rate from each of a plurality of extrusion orifices distributed around a circular extrusion manifold. More particularly, the invention relates to a set of cams mounted on a shaft which controls the size and shape of a set of extrusion orifices to compensate for feed rate variations.
2. Description of Related Art
When extruding masa, dough or other food product, there are often temperature and pressure variations over the cross-section of flowing extrudate as the extrudate approaches and exits extruder orifices. Such variations are especially prevalent with the use of an extruder manifold over which a plurality of extruder orifices is arranged. Additionally, variations in geometry and surface finishing contribute to non-uniform flow. Such variations cause extrudate exit velocity variations among the various extruder orifices which in turn yields product of varying length as product is extruded and cut from the orifices.
A frontal view of a typical prior art multiple-orifice extrusion manifold is shown in FIG. 1A. With reference to FIG. 1A, a cutting blade 108 rotates at a constant speed around a central axis 106 of a circular extrusion manifold 110. The cutting blade 108 cuts extrudate (not shown) as it exits pairs 102 of extrudate orifices 104 which form part of the extrusion manifold 110. Such a cutting blade or blades may make as many as 100 strokes per minute. As extrudate is pumped through the extrusion manifold 110, the velocity of extrudate exiting a top pair of extrusion orifices 120 may differ from the velocity of extrudate exiting a central pair 122 or bottom pair 124 of extrusion orifices. This difference is accentuated by the relatively high extrudate pressure necessary to pump the comestible extrudate through such an extrusion manifold 110, usually in the range from about 400 to 500 psi (2.7 to 3.4 MPa). The pressure drop across such a manifold 110 is usually in the range of 300 to 350 psi (2.0 to 2.4 MPa). As the extrudate is cut, the resulting pieces of extrudate vary in length in direct proportion to the variation in exit extrusion velocity. The result is product of varying lengths. However, for many applications, it is desirable to have a relatively uniform length of extrusion product.
A cross-sectional view of the extrusion manifold of FIG. 1A is shown in FIG. 1B. With reference to FIG. 1B, as extrudate (not shown) enters a flow path 114 leading to pairs 102 of individual orifices 104, variations in geometry, surface characteristics, pressure and temperature cause the linear flow to be non-uniform in portions of the flow path 114 around the central axis 106 despite great care of manufacturers to provide uniform paths to individual extrusion orifices 104.
According to the prior art, one method of adjusting for these differences is to stop the flow of extrudate, disassemble the manifold 110, and make adjustments to the size of the particular flow path 114 to various regions around the central axis 106 and to individual orifices 104. This is time consuming, iterative and imprecise. There exists a need for an improved device to individually adjust extrusion orifices to account for local variations in extrudate flow velocity. A need exists to compensate for varying temperature, pressure and velocity profiles in an extrudate flow up to and through extrusion openings. There exists a need to more accurately and quickly adjust the linear flow of extrudate through sets, pairs and individual orifices. The present invention fills these and other needs as detailed more fully below.